The invention concerns a wiper apparatus and a method for calibrating the contact force of a wiper arm.
Numerous wiper apparatuses for motor vehicles are already known in which a wiper blade attached to a wiper arm is pressed against the windshield of the motor vehicle with the aid of an extension spring to produce a wiper arm contact force. For this purpose, the wiper arm is attached in pivoting fashion to a rotary head using a hinge bolt, which rotary head is connected to the wiper shaft in torsion-proof fashion and makes an oscillating motion, for example. On the side facing the windshield, one end of the extension spring is thereby hooked in a bolt with one end at the wiper arm and with its other end on the rotary head. In such systems, the contact force can be varied or adjusted only by replacing the spring or one of the clamps holding the spring with another spring or another clamp.
The wiper apparatus has the advantage that the wiper arm contact force can be adjusted individually for any single wiper apparatus using an eccentric bolt as the calibrating element.
A relatively great deviation of contact forces between the individual wiper apparatuses in a series occurs as a result of tolerances of the spring rate and positional tolerances of the components that determine the arrangement of the spring and the spring preload itself. As a result of this, the mean contact force of all wiper apparatuses in a series must be specified such that a good wiping quality is also given when the contact force of the particular wiper apparatus moves on the margin of the tolerance range of the series. This is limited, on the one hand, by the wiper motor, because, due to its design, the contact force is used in the calculation linearly and, at maximum contact forcexe2x80x94i.e., maximum friction force of the wiper blade elementxe2x80x94the wiper motor must always remain capable of operating the wiper apparatus. On the other hand, the tolerance range is limited by the high-speed behavior. An acceptable wiping result must be achieved with a minimal contact force of the wiper arm and, therefore, the wiper blade, even at high speeds.
Using the calibrating element, a predetermined wiper arm contact force can be adjusted in very simple fashion, without using additional components or replacing them in entirety.
If one end of the wiper arm is connected to a rotary head in pivoting fashion, and the tensioning element between the wiper arm and rotary head is loaded, the contact force can be adjusted exactly, e.g., on a separate test stand, and the combination of rotary head, tensioning element and wiper arm can then installed on the wiper apparatus.
If the tensioning element on the rotary head is hooked around the eccentric bolt, it can be installed quickly, and it transfers the calibrating motion evenly.
In addition, if the tensioning element comprises at least one extension spring that is hooked around the eccentric bolt using a hook, then commercially-available, cost-effective extension springs can be used.
If the calibrating element comprises an external straight knurling for fixation purposes, then, in advantageous fashion, it cannot be twisted during operation as a result of the torque acting on the eccentric bolt, which would eliminate the calibration.
It is particularly advantageous if the calibrating element comprises a square socket or external square, a slit, or a cross recession for the calibration procedure. This is therefore easy to carry out using a commercially-available tool.
It is particularly advantageous, thereby, if the eccentric bolt is secured after turning. This can be accomplished, for example, by means of riveting, stamping, pressing or welding.
It is furthermore advantageous if the eccentric bolt comprises three cylindrical sections, whereby the two outer sections along its longitudinal extension comprise a coaxial centerline, and the center section comprises a centerlinexe2x80x94axis-parallel, in particularxe2x80x94that differs from the coaxial centerline. In this fashion, it is not only possible to change the preload of the tensioning element, it is also possible to change the preload of the torque acting on the wiper arm, because the distance between the spring force that acts on the axis-parallel centerline and the hinging bolt is changed when the eccentric bolt is turned.
If the two outer sections have different diameters, the eccentric bolt is easier to insert during installation and it is secured against falling out, for example. It is also advantageous hereby, of course, if the bolt comprises a chamfer on at least one side.
If the eccentric bolt can be inserted in the bore of the rotary head and comprises a partial straight knurling along one of its two outer sections, it is advantageous if the center section of the eccentric bolt is designed soxe2x80x94in particular, is at least so widexe2x80x94that the tensioning element can be hooked into the eccentric bolt without the straight knurling and bore being in contact. In this fashion, the eccentric bolt can be inserted into the bore during assembly, the tensioning element can be calibrated, and then the eccentric bolt can be prevented from turning by driving it home, because this creates a positive and non-positive connection between the bore and the eccentric bolt only after calibration is completed.
The advantage of the method xe2x80x94based on the inventionxe2x80x94according to claim 1 is that a positive connection is achieved between eccentric bolt and rotary head without having to sacrifice the accuracy of calibration, because the eccentric bolt can be driven home in any angular position.